For gas powered engines we've run the stock Kohler coils and made power up to 10,000 rpm so I don't know whats up. I think its probably because your running the wrong type of coils, you need to use the coils off of the 18hp Kohler Commnad, the ones with the rectangular side legs, not the ones with a cut out on them. We build our $2000 engine special for lawn mower racers and pullers all the time and use those coils with no problems at all, so as far as the Kohler coils don't work your all wet, but some types don't. I wouldn't condemn a product that works if you don't know all the facts about the various types under that name.
JE may stop making JR drag racing pistons that strange, but what in the world does that have to do with us. All of our pistons are custom made either from JE or Diamond for our application, we don't try to shoehorn in junk that it isn't made for it because we have it setting on the shelf.